The present invention relates to a process for producing negative copies with a light-sensitive or radiation-sensitive recording material comprising a layer support and a normally positive-working light-sensitive or radiation-sensitive layer. The normally positive-working layer contains, as essential constituents, a 1,2-quinone diazide and/or a mixture of a compound forming a strong acid under the action of actinic radiation and a compound having at least one acid-cleavable C-O-C group. The layer is irradiated imagewise, thermally treated, irradiated overall and then developed with an alkaline developer.
Positive-working light-sensitive compositions, in which the imagewise-irradiated areas become soluble and the non-exposed areas remain insoluble, are known in the art. Layers that are primarily used in practice to prepare materials of this kind have o-quinone diazides as the light-perfect sensitive compounds, and additionally contain resins with groups rendering them alkali-soluble, for example, phenolic resins.
Light-sensitive compositions based on acid-cleavable compounds are also known. The acid-cleavable compounds contained in these compositions comprise orthocarboxylic acid derivatives, monomeric or polymeric acetals, enol ethers or acylimino carbonates. As the radiation-sensitive compounds which split off acid the compositions usually contain organic halogen compounds, in particular s-triazines substituted by halomethyl groups. The binders employed also comprise resins having groups which render them alkali-soluble.
It is also known that a normally positive-working copying material based on an o-quinone diazide, in the presence of appropriate additives, can be used as a negative-working copying material by employing a particular sequence of treatments. GB 2 082 339 describes a reversal process of this kind, in which a light-sensitive composition comprising an o-quinone diazide and at least one resol is used as a negative-working recording material. DE 25 29 054, corresponding to U.S. Pat. No. 4,104,070, discloses resist layers based on 1,2-quinone diazides and containing a hydroxyethylimidazoline as an additive, for use in a reversal process. A similar material containing secondary or tertiary amines is described in U.S. Pat. No. 4,196,003. In the reversal process specified in EP 133 216, corresponding to U.S. Pat. No. 4,581,321, the additive contained in the o-quinone-diazide-containing copying layer comprises a hexamethylol melamine ether which is preferably used as a crosslinking agent in polymer reactions. EP 131 238, corresponding to U.S. Pat. No. 4,576,901, on the other hand, describes a reversal process, in which the light-sensitive material does not require any of the above-indicated basic or acidic additives. DE 37 11 263 and 37 25 949 disclose various s-triazine derivatives for use as substances which promote thermal hardening in reversal processes using normally positive-working formulations. From EP 082 463, corresponding to U.S. Pat. No. 4,506,006, a positive/negative reversal process is also known, which uses acid-cleavable compounds instead of 1,2-quinone diazides.
The known reversal processes basically comprise the same sequence of processing steps, i.e., the printing plate is heated after imagewise exposure, after cooling reexposed without original and then developed by means of an aqueous-alkaline developer. They are based on the fact that the light decomposition products produced form an insoluble reaction product upon heating. This thermal secondary reaction usually takes place in the presence of particular basic or acidic additives in the copying layer or in the presence of particular crosslinking agents containing multifunctional reactive groups.
For practical applications it is very important that the individual processing steps can be reliably performed and that, for example, imagewise irradiation, heating for image reversal, cooling, reexposure and development correspond to the conventional processing steps. A sufficient image reversal latitude should be ensured. The term "image reversal latitude" denotes the temperature range within which conversion can be carried out or the tolerance range of the time required for conversion.
The additives which have been described for compositions based on 1,2-quinone diazides can be classified as additives which, in the presence of the acid produced during irradiation, cause a thermal crosslinking reaction in the light-sensitive composition and basic additives which react to form a salt with the acid produced during irradiation and thus reduce the energy required for decarboxylating the acid (C. G. Willson: "Image Reversal: The Production of a Negative Image in a Positive Photoresist", Interface 82, San Diego 1982).
In a special embodiment, the additive used to extend the image reversal latitude is not a priori present in the radiation-sensitive layer, but is applied between the steps of imagewise exposure and thermal treatment, for example, by exposing the material to an ammonia atmosphere, as described, for example, in DE 35 41 451 and U.S. Pat. No. 4,775,609.
In the reversal treatment of a copying material, imagewise irradiation or exposure under an original is followed by heating without any further intermediate treatment, as is known. Heating can be carried out by irradiation, convection, contacting with heated surfaces, for example, rolls, or immersing into a heated bath of an inert liquid. The heating temperature varies in particular between 110.degree. and 140.degree. C. The heating step is followed by cooling the material to room temperature. Although the compositions generally withstand these temperatures it has, nevertheless, been found that thermal treatment gives rise to a fundamental disadvantage of this reversal processing, since it adversely influences the developing behavior of the radiation-sensitive layer. Developing times are, for example, usually markedly increased. In the case of mechanical processing according to fixed cycle times, this has the consequence that processing speeds, and thus plate throughput, must be considerably reduced and that, in some cases, reliable development is no longer possible, even at the lowest processing speeds.
To obviate this adverse influence of thermal treatment in an oven, it has already been proposed to carry out overall exposure under water (GB 2 188 448). This procedure eliminates the problems occurring in the development step. However, since construction of the apparatus required is difficult this solution is not yet practical.